it is very difficult situation for me when i have to use gender or sex terms.maybe to use gender term is more proper.but many english source using sex term referring to the gender.you know using sex term can be misunderstood.

As much as I know gender is for people only and sex is both for people and animals
Depending on where , how and why you use it , I do not think it will cause any trouble and as you have mentioned sex is more common:))

i think we shouldn't feel any hesitation or offence while using such words.people logical will see us.

I always use sex term not gender when i talk to my friends,so everyone can understand what i mean.I think you don't have to care that a lot.

I use this question ''m or f? '' :)